The invention relates to an anchor fluke. An anchor fluke forms that part of an anchor that has to produce the holding (counter) force necessary for the anchorage of an object. The anchor fluke is provided with means for attachment at the lower end of an anchor shank, which may have a rigid (plates) or flexible (cables, chains) construction and, at its upper end, is provided with means for attachment to the lower end of a penetration or anchor line, with which the anchor fluke can be drawn into the anchorage ground and be connected to the object that has to be anchored.
After having been lowered, the position taken up by the anchor fluke on the ground will not always be optimal for penetration into the anchorage ground. This may be the result of an asymmetric landing of the anchor fluke or an asymmetrically shaped basis (irregularities). Then, when the penetration line is hauled in, the anchor fluke will penetrate into the ground in an oblique manner, as viewed about the longitudinal axis or about an axis perpendicular to the fluke. In order to effectuate that the anchor fluke arrives back on course again and does not continue moving according to a penetration path that forms an angle with the penetration line, lateral forces on the anchor fluke will have to be generated. An oblique orientation may also be the result of areas in the anchorage ground having a different packaging density or composition. In that case, lateral forces must also be produced to restore the orientation of the anchor fluke.
During the initial penetration into the anchorage ground as well as during the further course of the penetration into said ground, it is therefore desirable to have the disposal of means with which said lateral, correcting forces are produced. To this end, many types of anchors and anchor flukes are equipped with stabilizers that correct a rolling and/or yawing movement of the anchor fluke.
A first example hereof is the anchor shown in U.S. Pat. No. 3,964,421 in the name of Van den Haak, wherein the substantially triangular flat fluke is provided with stabilizer plates at the rear edge at the corners, which stabilizer plates partially project sideways and of which the normal on the front planes is directed upwards to the front.
From European patent 49455 in the name of Van den Haak an anchor is known that, near the rear edge at the corners, is provided with stabilizer plates that project upwards and have front planes of which the normal is directed to the front and downwards, wherein the normals of the front planes of the stabilizer plates provided on either side are possibly facing away from one another.
From British patent 1,356,259 and European patent 0,020,152 an anchor is known, the fluke of which is a concavely bent, substantially triangular plate that, at its lateral edges, merges into concave, upwardly projecting tapering lateral plates, which form stabilizer surfaces that lie in a circular conoid converging backwards.
In WO 87/01347 a further development of the above anchor is described, in which the sides of the flat fluke are provided with lateral portions standing obliquely upright, onto which again substantially upright lateral plates are attached. Auxiliary flukes are transversely attached to said lateral plates, either on the outside or on the inside, which auxiliary flukes may serve as stabilizers. These stabilizer plates have front planes directed obliquely forwards and downwards.
Finally, from U.S. Pat. No. 4,433,635 an anchor is known, the fluke of which, at its rear end, merges into a stabilizer plate extending rearwards and sideways, which stabilizer plate inclines forwards and upwards with respect to the fluke.
All the discussed and known anchors are provided with stabilizer means or plates that may be considered to be extra parts with respect to the actual fluke or as projecting parts thereof. This will cause production costs of the anchors in question to rise. However, it is possibly more important that the protruding parts form objects that are easily damaged or may easily cause damage to other objects and have an unfavourable influence on penetration.
It is therefore an object of the present invention to provide an anchor fluke that corrects orientation and course with the least possible additions to the actual fluke and moreover shows improved penetration performance and has increased holding force.
To this end the invention provides an anchor fluke comprising a hollowe plate-shaped body, with attachment means for a shank and/or anchor lines, with a longitudinal axis and a front penetration edge and a rear trailing edge, which are located at a distance from one another in the direction of the longitudinal axis, wherein the fluke has a plane of symmetry that contains the longitudinal axis and is substantially perpendicular to the plate-shaped body, wherein the hollow plate-shaped body comprises an upper surface with a surface centre of gravity an a lower surface, which surfaces are bounded by the penetration edge, the trailing edge and lateral edges, and wherein said body, at the lower side, substantially between the edges, is provided with means for counteracting a rolling movement about the longitudinal axis during penetration of the anchor fluke in an anchorage ground and with means for counteracting a yawing movement about an axis that is perpendicular to the longitudinal axis and is located in the plane of symmetry during penetration in an anchorage ground.
In the anchor fluke according to the invention, the means for counteracting a rolling movement and a yawing movement are located on the lower side, at least substantially within the circumference of the actual fluke, while, during penetration, the ground can move freely across the upper surface of the fluke and the other penetration properties of the anchor fluke are therefore enhanced. The upper surface of the fluke is then at least almost fully available for providing holding force in cooperation with the ground.
The means for counteracting the rolling movement is preferably formed at least partially by planes of the lower surface of the fluke.
In that case the planes, viewed in longitudinal direction, preferably comprise first lateral areas of the lower surface of the fluke, which are located substantially behind the centre of gravity of the fluke, with surfaces that face downwards and forwards and possibly face one another. As a result of this arrangement, the form of the fluke is kept simple and the orientation of the fluke for penetration and during penetration is favourably influenced, since the means for counteracting the rolling and yawing movement keep the rear side of the fluke up and contribute to a foil-shape of the fluke.
The wing-shape of the fluke is further enhanced by second lateral areas at the lower surface of the fluke, located in front of the first lateral areas as seen in longitudinal direction, the second lateral areas having surfaces that face rearwards and downwards.
These surfaces, too, preferably face one another.
The anchor fluke is furthermore preferably provided with substantially vertical trailing plates that are located between the first lateral areas and the trailing edge and may form an integral part of the main longitudinal girders. These trailing plates form a means for counteracting a yawing movement during penetration of the fluke and diverge preferably rearwards with respect to one another. As a result, during an initial yawing displacement the correcting striking surface is enlarged and the counteracting striking surface is reduced.
The first lateral areas then enhance the action of the trailing plates in the correction of the yawing movement. They thus form bowl-like areas as it were, as a result of which the pressure that is exerted on the trailing plates by the ground to correct a yawing movement is increased.
According to a further development of the anchor fluke according to the invention, the lower surface of the fluke has a central area that extends upto the trailing edge, wherein said lateral planes extend at least partially until below the trailing edge of the central area. As a result a passage for soil is left clear, causing a favourable initial penetration performance to be obtained. In addition, said trailing plates may bound the earth flow canal in lateral direction. The trailing plates and said planes preferably extend in rearward direction until beyond the trailing edge of at least the central area. Owing to this, the (initial) penetration performance is further enhanced.